Raw water such as water from rivers, lakes or underground usually contains suspended matter. The suspended matter must be removed by clarification in order to provide water suitable for use in domestic and industrial applications. The suspended matter can consist of large solids, settleable by gravity alone without any external aid, and nonsettleable material, often colloidal in nature. Removal of the suspended material is generally accomplished by coagulation, flocculation, and sedimentation. in combination, these processes are referred to as conventional clarification. (see Betz Handbook of Industrial Water Conditioning, 9th Edition, 1991, Betz Laboratories, Inc., Trevose, Pa., pages 23 through 30).
Naturally occurring suspended particles are predominantly negatively charged. Water-soluble organic cationic polymers, such as polyamine and polydiallyldimethyl ammonium chloride, are normally used to clarify water having high turbidity (greater than 60 NTU, nephelometric turbidity units). In low turbidity water (less than 60 NTU), there are generally not enough particulates to form a settleable floc when the water is treated with cationic polymer alone. Inorganic coagulants such as aluminum sulfate, polyaluminum chloride, ferric sulfate, ferric chloride and sodium aluminate are used instead. These inorganic coagulants are relatively inexpensive and generally effective for water clarification. However, they tend to generate voluminous sludge which is difficult to dewater. Also, such inorganic coagulants are only effective within a particular pH range and therefore require proper pH adjustment of the water during treatment. In addition, residual iron and aluminum ions in the water treated may affect downstream operations such as cooling and boiler treatments and may also cause health and environmental concerns when the water is finally discharged.
Water soluble/dispersible melamine formaldehyde resins have been used for clarification of low turbidity waters, but the residual formaldehyde in the resin can give rise to handling and disposal difficulties. It is the object of the present invention to provide an effective method of clarifying water without incurring the disadvantages of inorganic coagulants and melamine formaldehyde resins.